The present invention was made under a contract with the Department of the Air Force. The invention is concerned with gallium phosphide photodetectors. In particular, the present invention is directed to gallium phosphide photodetectors which exhibit a large photoresponse for radiation of energies between about 2.8 eV and about 3.8 eV.
Gallium phosphide is a semiconductor material having an indirect bandgap of 2.24 eV and a direct bandgap of 2.8 eV. Visible wavelength photodetectors may, therefore, be made from gallium phosphide. Compared to cadmium sulfide and other visible wavelength detectors, much less work has been done on the photoconductive properties of gallium phosphide. Previous work has shown, however, that copper can act as a photosensitization center in gallium phosphide, yielding photoconductive gains as high as 10.sup.4 but with long response times. Among the references describing the photoconductive properties of gallium phosphide are G. W. Allen and R. J. Cherry, J. Phys. Chem. Solids 23, 509 (1962); H. G. Grimmeiss and H. Scholz, Philips Res. Reports, 20, 107 (1965); P. Goldstein and S. S. Perlman, Phys. Rev., 148, 715 (1966); D. L. Bowman, J. Appl. Phys., 38, 568 (1967); D. F. Nelson et al, Phys. Rev., 135, A1399 (1964); and U.S. Pat. Nos. 3,261,080 and 3,412,252.